Tear film break-up time
Dry eyes can have many causes. These range from the “simple” – blepharitis – to autoimmune diseases and hormonal disorders. Dry eye is not usually dangerous, but it can severely limit the quality of life of the patients affected by it, and the objective is to generate a healthy tear film that evaporates slowly and has a normal “tear film break-up time”.
Normal tear film
Resists evaporation for over 10 seconds
Morbid tear film
Breaks down after a few seconds (black spots)
Tears get produced – but they also get drained into the tear duct. It’s a dynamic process, and it’s good to understand how quickly the tear film is being drained. The amount that’s being drained any given time can be determined by measuring the tear meniscus with a high-resolution camera.
An analysis of the meibomian glands in the lid margin allows to determine the best therapy for you.
We can determine the quality of the tear film with a Placido disk analysis. You look at concentric rings; a camera at the centre of the rings takes an image of what’s reflected back from the surface of the eye. The presence (or absence) of distortion in these rings provides information about the quality of the tear film.
Tear film osmolarity
If you have a salt solution and boil off (evaporate away) all of the water, you generate an increasingly salty solution until only the salt is left. It’s the same with evaporative dry eye: the increasing saltiness (osmolarity) indicates the severity of dry eye.